Structural and functional differentiation of the embryonic chick pineal organ in vivo and in vitro

Abstract

The development of sensory structures in the pineal organ of the chick was examined by means of scanning electron microscopy from embryonic day 10 through day 12 post-hatching. At embryonic day 10, the wall of the tubules within the pineal primordium is composed of cells with unspecialized luminal surface. Differentiation of sensory structures starts at embryonic day 12 when pinealocytes and supporting cells can be distinguished. Pinealocytes are recognized by virtue of an inner segment only rarely endowed with a cilium, whereas supporting cells exhibit numerous short microvilli. Further differentiation of the sensory apparatus is achieved by development of an oval-shaped, biconcave swelling at the tip of the cilium, 1 x 2 microns in size, and a collar of long microvilli at the base of the inner segment. Membrane specializations of sensory cilia, however, were not detected. Since during embryonic life new tubules and follicles are continuously formed, all stages of differentiation of sensory structures are found in the chick pineal organ during the second half of the incubation period and the first two weeks after hatching. In 200-microns-thick Vibratome sections of chick-embryo pineal organs cultured in medium BM 86 Wissler for periods up to 13 days the cytodifferentiation parallels the development in vivo. Using an organ-culture system the 24-h release of melatonin into the culture medium was measured by means of radioimmunoassay after solid-phase extraction. At embryonic day 10, the 24-h secretion of melatonin was at the lower range of detection of the RIA (5 pg). The rapid increase in 24-h secretion in melatonin until hatching (approximately 50 micrograms) is approximated by an exponential curve.

Regulation of melatonin secretion in the pineal organ of the domestic duck – an in vitro study

“…Up till now, the embryonic development of the avian pineal organ has been investigated exclusively in chick and quail embryos. The release of trace amounts of MLT from the chicken pineal organ in vitro was detected as early as on the day 11 of embryonic life, and a large increase in the secretion level was observed during the subsequent days of development (Möller and Möller 1990). The regulation of MLT synthesis by light acting via pineal photoreceptive structures was found for the first time in 13-14-day-old chick embryos (Akasaka et al 1995, Lamosová et al 1995, Csernus et al 2007).…”

Immunoelectron-microscopic investigation of the subcellular localization of pinopsin in the pineal organ of the chicken

“…For this purpose, conventional transmission and scanning electron microscopy has been used (cf. Oksche and Vaupel-von Harnack 1966;Oksche and Kirschstein 1969;Oksche et al , 1972Boya and Zamorano 1975;Omura 1977;Calvo 1978, 1980;Matsuo 1984, 1988;Möller and Möller 1990). In these studies, typical photoreceptor cells with regular comb-like arrangements of outer segment membranes have not been identified, although basic sensory structures such as bulbous cilia with associated lamellar complexes have been observed (Menaker and Oksche 1974;Vollrath 1981).…”

Differentiation of pinopsin-immunoreactive cells in the developing quail pineal organ: an in-vivo and in-vitro immunohistochemical study

“…1E). The former probably corresponds to the supporting cells and the latter to the pinealocytes as described in the avian pineal follicles in situ (Oksche et al 1972;Möller and Möller 1990). Both Rho-LI and Pino-LI cells occurred among the round cells.…”